1. Field of the Invention.
The present invention relates generally to railway signaling and more particularly, to rail break or vehicle occupancy detection on railroad track. More specifically, the present invention is in the technical field of railroad signaling and train control, including positive train control (PTC), centralized traffic control (CTC), automatic block signaling (ABS), communications-based train control (CBTC) and cab signaling.
2. Background of the Invention.
Conventional railway wayside signaling systems employ the rails of the track for transmission of signals used to detect track occupancy, broken rail and/or open turnouts. Railroad track is physically divided into a plurality of electrically-distinct blocks, each block having a track circuit typically terminated by insulated joints and equipped with bi-directional track code transceivers. It should be understood that the term “code transceiver” should be broadly construed to include any type of track circuit signal transceiver or cab signal transmitter. The code transceivers typically send and receive low-frequency, pulse-modulated carrier signals through the track circuit, thereby communicating signal status to each other. The presence of a train in the block causes the rails to be shunted, interrupting this communication, while the presence of a broken rail in the track causes an open circuit, also interrupting this communication. Additionally, turnouts in the track may be wired such that when not aligned for the normal route, communications will be interrupted. This is commonly known as an open turnout.
A fundamental limitation of fixed-block track circuit systems is their inherent inability to detect a rail break that is located behind a moving train within the same block as the train. Since many rail breaks occur under a train, it would be highly desirable to have the ability to detect broken rail behind a train within the block it is occupying. This would allow immediate notification of a following train or other entity, such as a train dispatching system or back office server.
Another limitation of fixed-block track circuit systems is the inability to detect where within a block an occupancy exists. Therefore, the entire block must be assumed to be occupied from the perspective of the signaling system. This inability to distinguish a track occupancy from a rail break, and the inability to locate where the occupancy or break is within the block artificially limits maximum traffic density on the track and therefore fundamentally restricts how efficiently a given track can be utilized. It would be highly desirable to have a true “moving-block” or “virtual block” train control system, including the ability to detect rail breaks, open turnouts or occupied track behind a train's current position within the same block that the train occupies, enabling the full potential benefit of CBTC implementation.
The present invention at least partially overcomes these limitations by using equipment on the leading or trailing end (if so equipped) of a railway vehicle to detect conventional track code or cab signal code in the track, and thereby determine if the track ahead of or behind the vehicle, but still in the same block, is occupied or has a broken rail. Information regarding reception of these signals is then transmitted over a wireless RF link to following trains, possibly via one or more wayside systems or a central office system and correlated with train location information, giving a positive, fail-safe closed-loop indication of rail integrity and the extent of track vacancy. This information may be used in the generation of movement authorities or restrictions for trains as an integral part of a CBTC or PTC system, allowing a fail-safe implementation of a moving-block or virtual block train control system.
In some embodiments of the present invention, the wayside signal equipment is customized to provide additional pulsed codes assigned to a series of blocks to give a vital indication of which track a vehicle is occupying, thereby facilitating determination of vehicle location in a CBTC or PTC system.
In some embodiments of the present invention, the current present in the track circuit of each block is monitored at each wayside track code transceiver. By appropriately correlating, using an RF link, the current measurements with the pulsed carrier signals and the carrier signals received by the vehicle, it is possible to distinguish a track occupancy from a rail break ahead of or behind a vehicle. This information may form an integral part of a CBTC or PTC system.